Browserstack and SauceLabs are older in the industry, have a significant market share, and offer multiple features and integrations. Still, users complain about some performance issues with launching VM's for tests, and pricing is not as competitive as the new arrivals in the space.

LambdaTest has the advantage of an always free plan, that allows you to use all available features (only resources and available server time is limited).
Also starting price is more affordable (15 USD vs 19 or 25 for competitors). Even the full package price is better (with all automation and tools you need).

LambdaTest has better user ratings, and it's integrated with way more tools and platforms, so it would be easier to integrate it into your normal development or testing process.

We recommend to try all of them, and decide which one is better suited for you.